This is a 371 of PCT/DE 01/00400 filed Feb. 1, 2001.
The present invention pertains to a rubber bearing characterized by improved absorption of loads which occur as a consequence of torsion and cardanics. It preferably pertains to simple rubber bearings in which the coaxially arranged insert parts are adherently connected to one another by means of the elastomer. However, the general consideration of the present invention is also applicable to multipart rubber bearing or those in which additional insert parts or stop disk are provided for certain purposes.
Rubber bearing are used for a very great variety of purposes mainly in the manufacture of vehicles. Depending on the particular intended use, greatly different requirements are imposed on the bearings in terms of loadability. In particular, bearings which are used in the area of the chassis, e.g., in connection with the wheel suspension, are also subject to a high load due to torsion or cardanics. It is therefore necessary the adapt the bearings to these loads in terms of their axial and radial rigidity.
Without additional measures, simple rubber bearings of the conventional design have a xe2x80x9cnaturalxe2x80x9d ratio of about 1:3 between the axial rigidity and the radial rigidity. To change this ratio in terms of a better adaptation to the cardanic loads or torsional stress which occur, it has hitherto been necessary to provide complicated insert parts or stop disks for the bearings. This leads to sometimes rather complicated designs. In addition, such parts will in turn lead to undesired limitations in other areas in terms of the conversion of torsion and cardanics. The complicated design leads to complicated manufacture and consequently high manufacturing costs. Furthermore, there are high expenses for the testing and the design of corresponding test set-ups. The assembly at the user, especially the accurate adjustment in terms of the directional loadability, is also comparatively complicated.
A rubber bearing which guarantees the improved absorption of forces introduced axially due to a special shape of its inner part and of the outer sleeve is described in DE 28 38 391 A1. The jacket surfaces of the inner part and of the outer sleeve are sloped against the axis of the bearing in this bearing. When axial forces are introduced, the inner part and the outer sleeve are radially displaced in relation to one another due to their special shape. However, a bearing designed according to this document cannot be considered for use for each intended purpose, especially concerning the shape of its outer sleeve.
An elastic bearing for absorbing cardanic deflecting movements has been known from DE 33 46 665 A1. According to the solution described, hollow recesses are prepared in the joint body on both front sides of the joint. As a result, there is restricted guiding for the joint body when cardanic deflecting movements occur.
The object of the present invention is to provide a rubber bearing which, having a simple design, can be varied within broad limits in terms of the ratio of the axial rigidity to the radial rigidity and can thus be adapted to the particular intended use, especially in terms of loads due to torsion and/or cardanics which may possibly occur.
The object is accomplished with a rubber bearing having the features of the principal claim. Advantageous variants and embodiments of the bearing according to the present invention are described by the subclaims.
The rubber bearing, which is preferably designed as a simple rubber bearing, comprises in the known manner an essentially cylindrical inner part, a tubular outer sleeve arranged coaxially around the inner part as well as a pressure body, which is formed by an elastomer, is arranged between the inner part and the outer sleeve and is connected to them by vulcanization. The inner part and the outer sleeve of such rubber bearings usually have a cylindrical shape. However, the shape may also deviate from this for certain applications; for example, the cross-sectional area may also have an elliptical shape or a shape similar to the elliptical, or the parts may have shoulders in the course of their axial extension. The applicability of the basic idea of the present invention remains unaffected hereby. In the manner according to the present invention, two free grooves of a special shape, which extend in the axial direction into the interior of the bearing and extend over a complete circle around the axis of the bearing, are prepared in the elastomer, beginning from the axial ends. The special shape of the free grooves is that their radial distance from the axis of the bearing and/or their width changes cyclically and that there is a phase shift in terms of their course, which is determined by the change in the radial distance from the axis of the bearing and/or the width. The course of both free grooves preferably follows the same cycle. In addition, the strands of equal axial loadability form a cross bond due to extending in alternating directions according to the present invention in the pressure body formed by the elastomer. The fact that the ratio of the radial rigidity to the axial rigidity can be varied in a very simple manner in bearings having otherwise basically the same design by setting the angles of the strands forming the cross bond in relation to the axis of the bearing and/or by a different shape of the course of the contours of the free grooves can be considered to be essential for the present invention. It is also within the scope of the present invention if, in addition, the axial depth of both free grooves relative to the circumference of the bearing varies and both protrude into the interior of the bearing beyond the axial center at least in some sections. The phase shift existing between their courses is selected to be such that the bottoms of the free grooves have a different radial distance from the axis of the bearing in the sections of the circumference of the bearing in which both free grooves extend beyond the center of the bearing. The ratio of the axial rigidity to the radial rigidity of the bearing can be set in the range of 1:3 to nearly 1:1 by correspondingly setting the angles of the strands forming the cross bond and/or the geometry of the free grooves.
Corresponding to a possible embodiment of the bearing, the cyclically changing distance between the free grooves and the axis of the bearing is determined by an approximately sinusoidal course of their inner contour. This inner contour is in turn determined by the particular material thickness of the elastomer in the area of its connection to the inner part of the bearing. Another possible embodiment is represented by a corresponding course of the outer contour of the free grooves. The material thickness of the elastomer likewise has a sinusoidal course in the area of its connection to the outer sleeve. This ensures a corresponding cyclic variation of the width of the free grooves. In addition, a combination of the two possibilities described above leads to an obvious possible embodiment due to the fact that both the inner contour and the outer contour of the free grooves have a sinusoidal course. Due to a corresponding phase shift between the two sinusoidal contour courses, this embodiment variant leads to free grooves in which the distance between the course of the free groove and the axis of the bearing changes according to a sinusoidal pattern while the width remains constant.
The sinusoidal course of the inner and/or outer contour of the free grooves advantageously extends over at least two cycles. This means that at least two points of maximum material thickness and two points of minimum material thickness of the elastomer are present in the course of the contour in the area of the connection between the elastomer and the inner part and/or the outer sleeve.
Particularly advantageous is an embodiment of the bearing in which the cross bond between the strands of equal axial loadability is designed such that a first strand of the contour of the free groove is connected to an axial end of the inner part of the bearing and the outer sleeve, while a second strand, which crosses the first one at an angle, is connected to the other axial end of the inner part of the bearing as well as to the outer sleeve. Corresponding to an advantageous variant of the bearing according to the present invention, axially extending openings may be provided in the pressure body formed by the elastomer. It is possible due to this measure to impart different radial rigidities to the bearing in its circumferential direction. Another advantageous possibility of influencing the behavior during torsion or cardanic load is offered by a variant of the bearing according to the present invention, in which local bulges are provided on the strands which determine the contours of the free grooves. These bulges make possible an even better distribution of the stresses occurring during torsion or cardanics in the bearing. These bulges are preferably provided for this purpose on the inner contour of the free grooves in the area surrounding the points of greatest material thickness of the elastomer in the area of its connection to the inner part. The present invention will be explained in greater detail below on the basis of an exemplary embodiment.